Light translating device



July 11, 1961 P. T. FARNSWORTH 2,992,346

LIGHT TRANSLATING DEVICE Original Filed May 7, 1952 1 1 I 1,/////////////////////////w/////////// 4 g 5 6 I5 7? 205] HIM INVENTOR.

PHILO 7T FARNSWORTH ATTORNEYS electron image emitted by thephotocathode.

United States Patent 4 Claims. (Cl. 31367) This is a continuationapplication for co-pending Farnsworth application Serial No. 286,583,filed May 7, 1952, and now abandoned.

This invention relates generally to electronic light translating devicesand more particularly to such devices for translating a radiation image(infra-red or visible) of a given intensity into a light image ofgreater intensity, or for producing from a light image of a givenduration at light image of another duration.

Devices are known which convert an infra-red light image into acorresponding visible light image. In many instances the intensity ofthe resultant visible light image is less than desired. Likewise whenthe infra-red light image is of short duration, as when stroboscopicflashing is employed, the resultant visible light image is often toobrief for adequate viewing.

An object of the present invention is the provision of an improvedelectronic device for translating a light image of a given intensityintoa light image of greater intensity.

Another object of the present invention is the provision of anelectronic device adapted to translate a light image of brief durationinto a light image of greater duration.

A further object of the present invention is the provision of anelectronic device for translating an infra-red light image into acorresponding visible light image which produces an intensified visiblelight image and is adapted to store and produce from brief infra-redlight images, visible light images of greater duration.

In carrying out my invention, a photocathode is arranged to receive theimpinging light image and to release a corresponding electron image.This electron image is focused on a separate storage electrode to prducethereon a corresponding electrostatic charge pattern or image. Thestorage electrode is provided with a multiplicity 'of small openings andfor this purpose may be in the form of a fine mesh screen. A spray ofelectrons (from a flood cathode) is directed through the screen openingsand the number of electrons passing through the openings is controlledby the electrostatic charge on the portion of the screen surroundingeach opening. Thus there is produced an extended electron image of anintensity which varies in its elemental areas in accordance with thecorresponding charges on the screen. Under proper operating conditions,the extended electron image is of greater intensity than the originalThis intensified electron image is then directed onto a fluorescentscreen to produce a correspondingly intensified light image. It will benoted that even if the duration of the incoming light image is short,the intensified light image may be of greater duration due to thestorage of the electron image or the storage electrode.

It is to be noted that in accordance with the present invention thephotocathode and the storage electrode are separate electrodes and arespaced from each other instead of being combined into a singleelectrode. This provides numerous advantages. Broadly speaking, thisenables optimizing the characteristics of each of the electrodes toserve its respective function best. Thus, for example, the surface ofthe photocathode is continuous so that none of its effective area islost in insulav Patented July 11, 1961 tion between separatephotocathode electrodes. Migratory caesium atoms of the photocathodewhich would affect the leakage of the storage screen in an unpredictableand hardly controllable manner cannot affect this leakage when thephotocathode and storage screen are separate. [If a thermionic floodcathode were employed to provide a large image current, various problemswould be introduced into the photocathode, such as cathode fatigue,etc., if the photocathode and the storage electrode were combined.

Accordingly a further object of the present invention is to provide animproved device for translating a light image into a more intense lightimage in which the means responsive to the incoming light image forproducing an electron image is separated and spaced from a means forstoring the electron image in the form of an electrostatic image.

The foregoing and other features and objects of this invention and themanner of attaining them will become apparent and the invention itselfwill be better understood, by reference to the following description ofan embodiment in which the drawing is a schematic representation of anelectron discharge light image translating device together withassociated apparatus.

Referring now to the drawing, the electron discharge device 11 isprovided with an evacuated envelope 2 which contains various electrodesto be described hereinafter. As represented in the drawing, a lightimage fiom an object 3 is focused by means of a suitable lens 4(indicated schematically) onto a photocathode 5, which in response tosaid light image emits a corresponding electron image. This electronimage is directed by suitable means, such as by accelerating electrodes6 and 7 and focusing electrode 8, onto a storage electrode 11. Thiselectrode 11 consists essentially of a thin plate 12 of insulatingmaterial having fine mesh openings, as in a screen. Preferably, theinsulating material 12 consists of a coating of dielectric material onthe side of a fine wire screen mesh screen 13, the dielectric materialfacing the photocathode 5. The dielectric coating is provided withopenings in registry with the wire mesh screen openings. The fine Wiremesh screen 13 may be used for purposes of mechanical support, forerasure of the electrostatic charge on the insulation, or forcontrolling the degree of electron penetration. The storage electrode 11may be of the type shown and described in my corresponding US.application for Cathode Ray Tube and System, Serial No. 197,612, newPatent No. 2,754,449, filed November 25, 1950. The electrons fromphotocathode 5 are preferably given a sufficient velocity by the voltageon the accelerating electrodes so as to produce a secondary emissionfrom the insulation 12 which is greater than unity, thus producing apositive electrostatic charge image on the insulation 12 correspondingto the electron image from photocathode 5. Electrode 8 in addition toits focusing function serves as a flood cathode and for this purpose maybe coated with the usual emissive barium-strontium oxides on the side 14facing the storage electrode 11. Electrode 8 may be energized by anysuitable means such as by a heating coil 15. Electrode 8 has an opening16 in the center which is at the cross-over point of the electron imageemitted from the photocathode 5. Electrons from the flood cathode 8 passthrough the accelerating electrode 7 and spray the entire surface of theelectrode 11. The electrostatic charge on the insulation 12. controlsthe flow of flood electrons through the screen openings to produce anamplified extended electron image which may be projected onto thefluorescent screen 18. Stated in other words, electrode 11 resembles thegrid of an amplifying tube (as more fully described in said US.application Serial No. 197,612, new Patent No. 2,754,449), so that theelectrons from flood cathode 8 that pass through the electrode 11produce an amplified electron image on the right side of the electrode11. This amplified image is accelerated by electrode 17 and directedonto the screen 18 coated with suitable phosphors. The amplifiedelectron image is thereby translated into an amplified light image.

Erasure of the electrostatic charge image may be accomplished by leakagefrom the insulating material 12 onto screen 13, by varying the potentialof the electrons issuing from flood cathode 8 to produce such erasure,or by other means well known in the art.

An advantage of the arrangement just described is that even though theinput light image of object 3 is so brief that it cannot be discerned bythe human eye, because of the development of the correspondingelectrostatic charge image on storage electrode 11, the amplified lightimage produced on screen 18 will be of longer duration so that in effectthe brief input light image is extended in duration as viewed on screen18. The persistence of the electrostatic charge image on storageelectrode 11 is controllable by the particular material used for thedielectric coating 12, the coating thickness, and the coating shape, aswell as the potential on screen 13 as will be recognized by one versedin the art.

In accordance with another feature of the present invention, use is madeof the above phenomena by providing a stroboscopic light source 19 whichflashes light, visible or infra-red, onto the object 3, under thecontrol of the usual stroboscope control means 20. In order that thedevice 1 will respond only to the reflected stroboscopic light fromobject 3, control device 20 momentarily renders device 1 inoperative,for example, by removing the accelerating voltage from acceleratingelectrode 6. Other means for preventing operation of device 1 willreadily occur to those versed in the art. It will thus be seen that veryshort flashes of stroboscopic light will suffice to produce a lightimage of object 3', which though extremely short in duration will, bymeans of the device 1, produce a light image (on screen 18) ofsuflicient duration to be clearly seen or studied.

While the [foregoing description has given specific details of anembodiment of my invention, it will be apparent that numerous changesmay be made in these details without departing from the spirit thereof.The specific structure of storage electrode 11 can be changed in variousways within the scope of the present invention and still produce thecharge image and the amplifying action herein described. Changes in thefocusing system are obvious. Furthermore, while I have described astorage screen that is charged positively by the primary electrons ofthe electron image, the screen may be charged to produce a resultingnegative electrostatic image and the device may thus operate in thismanner as an amplifier, the theory of operation being similar to thatdescribed in my U.S. Patent No. 2,257,942 issued October 7, 1941, forImage Amplifier.

Accordingly, while I have described above the principles of my inventionin connection with specific apparatus, it is to be clearly understoodthat this description is made only by way of example and not as alimitation to the scope of my invention.

What I claim is:

1. A system for viewing objects comprising a source of radiation flasheswhich may be trained on a viewed object for obtaining reflectedradiation images of said object of short duration, a viewing devicecomprising a photoelectric cathode responsive to said reflected imagesfor producing corresponding electron images, a storage electrode forstoring said electron images for a predetermined period of time, a floodcathode positioned to flood said storage electrode with electrons whichare modulated in accordance with the stored images taproduce secondaryelectron images, a luminescent screen responsive to'said secondaryelectron images for reproducing instantaneously all elements of saidelectron images into corresponding light images, and a signal generatoroperatively coupled to said viewing device and said source, said signalgenerator controlling the flashing of said source and the operationof'said viewing device in such a manner that said photocathode iseffective only during reception of a reflected image.

2. A system for viewing objects comprising a source of radiation flasheswhich may be trained on a viewed object for obtaining reflectedradiation images of said object of short duration, a viewing devicecomprising a photoelectric cathode responsive to said reflected imagesfor producing corraponding electron images, a storage electrode forstoring said electron images for a predetermined period of time, a floodcathode positioned to flood said storage electrode with electrons whichare modulated in accordance with the stored images to produce secondaryelectron images, a luminescent screen responsive to said secondaryelectron images for reproducing instantaneously all elements of saidelectron images into corresponding light images, and a signal generatoroperatively coupled to said viewing device and said source, said signalgenerator providinga signal which prevents the photoelectric image fromimpinging said storage elec trode, and further controlling the flashingof said source, the flashing of said source and control of saidphotoelectric image being synchronized such that said storage screen ischarge with an image only during the time said cathode is receiving areflected image.

3. A radiation image reproducing device comprising a photoelectriccathode arranged to receive a radiation image and to produce a firstelectron beam responsive thereto defining a first electron image, aluminescent display screen spaced from said cathode and responsive to asecond electron beam defining a second electron image for reproducingthe latter in visible form, an electron image storage screen interposedin alignment between said cathode and said luminescent screen, electronlens elements arranged to focus said first electron beam from saidcathode onto said storage screen, said storage screen being sensitive tosaid first electron beam to provide a charge pattern corresponding tosaid first electron image, said storage screen being of reticulate formand including a dielectric material, and a flood cathode having anemissive area at least as large as said storage screen and beinginterposed in alignment between said photo-electric cathode and saidstorage screen for flooding the latter with a flood beam of electrons,said flood cathode being positioned at the crossover point of said firstelectron beam from said photo-electric cathode and having a relativelysmall, centrally located aperture formed therethrough arranged to passsaid first electron beam, the electrons from said flood cathode passingthrough said storage screen and being modulated by the latter to producesaid second electron beam and thereby said second image.

4. A radiation image reproducing device comprising a photoelectriccathode arranged to receive a radiation image and to produce a firstelectron" beam responsive thereto defining a first electron image, aluminescent .display screen spaced from said cathode and responsive to asecond electron beam defining a second electron image for reproducingthe latter in visible form, an electron image storage screen interposedin alignment between said cathode and said luminescent screen, electrodelens elements arranged to focus said first electron beam from saidcathode onto said storage screen, said storage screen being sensitive tosaid first electron beam to provide a charge pattern corresponding tosaid first electron image, said storage screen being of reticulate formand including a dielectric material, and an electrode interposed inalignment between said photo-electriccathode and said storage screen atthe crossover point of said first. electron beam and ham ing arelatively small, centrally located aperture formed therethrough forpassing said first electron beam, said last- References Cited in thefile of this patent UNITED STATES PATENTS McGee Sept. 2, 1941 Iams June22, 1943 Sziklai Feb. 22, 1949 Schlesinger Dec. 5, 1950 Somers -l Sept.23, 1952 Russell et a1 May 19, 1953 Sheldon Mar. 20, 1956 Henderson Oct.2, 1956

